Google has been using 3 performance metrics to rank websites since 2021. If your site is slow or unstable, you're losing positions — and clients. Here's how to test your site in 5 minutes and understand your results, even without being a developer.
The 3 Core Web Vitals explained without jargon
Google measures the quality of user experience on your site through 3 precise metrics. Here's what they actually mean:
LCP — Largest Contentful Paint
In plain English: how long does it take for the main content of your page to become visible?
The analogy: imagine walking into a restaurant. LCP is the time between opening the door and being able to read the menu. If you wait 6 seconds to see the menu, you walk out.
LCP measures the loading time of the largest image or text block visible on your page. On a brochure site, this is typically your hero image or main headline.
INP — Interaction to Next Paint
In plain English: how long does your site take to respond when you click something?
The analogy: you press a lift button. INP is the time between pressing and the button lighting up to confirm. If nothing happens for 2 seconds, you press again — and start getting annoyed.
INP replaced FID in 2024. It measures the site's overall responsiveness to all interactions (clicks, taps, keyboard inputs) throughout the entire visit.
CLS — Cumulative Layout Shift
In plain English: do elements on your page move around while it's loading?
The analogy: you're reading an article online, you go to click a link — and just as you click, an ad loads and shifts the link 3 centimetres down the page. You click the wrong thing. That's exactly what CLS measures.
A high CLS score means your visitors are clicking on elements they didn't intend to — a frustrating experience that drives users away and penalises your SEO.
How to test your site right now
You can test your Core Web Vitals in under 5 minutes using free tools:
1. PageSpeed Insights (recommended)
Go to pagespeed.web.dev (free official Google tool). Enter your homepage URL and click "Analyse".
You'll get:
- A score from 0 to 100 for mobile and desktop (separately)
- All 3 Core Web Vitals with their measured values
- A list of improvement opportunities ranked by potential impact
Tip: test the mobile version first. Google uses mobile-first indexing — your mobile score influences your SEO ranking.
2. Google Search Console — "Page Experience" report
If you have access to Google Search Console (recommended for every site owner), the "Page Experience" report shows you real data collected from your actual visitors — not a simulation, but real field measurements.
To access it: Search Console → Experience → Core Web Vitals.
3. Chrome DevTools (for deeper analysis)
In Chrome, press F12 → "Lighthouse" tab → select "Performance" and "Mobile" → click "Analyse page load". Useful for testing pages not yet live.
Understanding your scores: green, orange, red
Here are Google's official thresholds for each metric:
| Metric | 🟢 Good | 🟡 Needs improvement | 🔴 Poor |
|---|---|---|---|
| LCP (loading) | ≤ 2.5 s | 2.5 – 4 s | > 4 s |
| INP (responsiveness) | ≤ 200 ms | 200 – 500 ms | > 500 ms |
| CLS (stability) | ≤ 0.1 | 0.1 – 0.25 | > 0.25 |
Goal: have all 3 metrics in the green. A single red score can be enough to lose positions to a competitor with everything in the green.
Starting situation: cosmetics e-commerce, 8,200 visits/month, mobile PageSpeed score 38/100. LCP: 6.8 seconds. CLS: 0.42 (many elements shifting during load). Conversion rate: 1.2%.
Optimisation over 3 weeks: image compression and WebP conversion, lazy loading, migration to faster hosting, CLS element fixes (missing image dimensions, preloaded fonts), removal of 4 non-essential third-party scripts.
Results: mobile score rose to 91/100. LCP: 1.9 seconds. CLS: 0.06. Business impact: +34% conversion rate, -28% bounce rate, monthly revenue +45% in the 8 weeks following optimisation.
What most often kills your scores
In 80% of cases, poor Core Web Vitals scores come from the same sources. Here are the most frequent culprits, from most to least common:
- 🖼️ Heavy, unoptimised images: problem #1. A 3MB JPG image that could weigh 200KB as an optimised WebP. Use tools like Squoosh (free, online) or configure your CMS to serve WebP automatically. Always define width and height attributes to avoid CLS.
- 📦 Too many plugins and third-party scripts: each WordPress plugin loads CSS and JavaScript files. Every social media widget, chat tool, analytics tracker — all block or delay page rendering. Audit your plugins: remove unused ones, replace heavy plugins with lightweight alternatives.
- 🖥️ Slow hosting: shared hosting at £5/month with hundreds of other sites on the same server mechanically generates slow response times (high TTFB). This is often the root cause of a poor LCP. Migrating to VPS or managed hosting (WP Engine, Kinsta, SiteGround) can double your scores overnight.
- 💾 No caching: without cache, every visitor triggers dynamic page generation. Activate a caching plugin (WP Rocket, W3 Total Cache) or a CDN (free Cloudflare) to serve pre-generated static pages.
- 🔤 Render-blocking web fonts: Google Fonts or other web fonts loaded via
<link>in the<head>block page display until they download. Solution: host fonts locally and addfont-display: swap.
When should you call a developer?
Some optimisations are accessible without technical skills. Others require professional intervention:
You can handle yourself:
- Compress images before uploading (Squoosh, TinyPNG)
- Disable unused WordPress plugins
- Enable Cloudflare (free CDN caching)
- Update your WordPress plugins and theme
Call a developer if:
- Score < 50/100 — the problems are structural, not just settings adjustments.
- Hosting is the problem — migrating a WordPress site without losing data or SEO rankings requires technical expertise.
- WordPress with 30+ active plugins — a performance audit with theme refactoring and replacement of heavy plugins requires deep ecosystem knowledge.
- Good desktop score but poor mobile score — usually a non-responsive images problem or blocking resources that requires code.
Core Web Vitals are measured on real field data (CrUX — Chrome User Experience Report). A good lab score (PageSpeed Insights) doesn't guarantee a good field score. If your page has little traffic, Google may lack real data — focus on lab scores in that case.
FAQ — Core Web Vitals 2026
My site scores 85/100 on PageSpeed — is that enough?
85/100 is a good score — in the green zone. For a brochure or professional site, it's sufficient to avoid Google penalties. For e-commerce or highly competitive markets, aim for 90+ on mobile to maximise conversions. The key is having all 3 Core Web Vitals in the green — an overall score of 85 with a red CLS is worse than a score of 78 with everything in the green.
Do Core Web Vitals actually affect my Google ranking?
Yes. Google has officially used them as a ranking factor since 2021 through the "Page Experience" signal. In practice, their impact is strongest in competitive markets where content is equivalent — that's when speed and stability make the difference. Case studies show gains of 5 to 20 positions for optimised pages. On high-value commercial queries, that's directly traffic and revenue.
How much does Core Web Vitals optimisation cost?
From £500 for simple fixes (image compression, cache activation, Cloudflare) to £2,500–£4,500 for full optimisation including hosting migration, technical refactoring and complete audit. ROI is measurable in weeks — the case study above illustrates a return on investment of over 500% in under 2 months.
Can WordPress achieve 90+ on PageSpeed?
Yes, absolutely. With the right setup: fast hosting (WP Engine, Kinsta, SiteGround), lightweight theme (GeneratePress, Astra), fewer than 15 active plugins, optimised WebP images, and a CDN (Cloudflare). WordPress sites regularly achieve 95+/100 with these configurations. It's a configuration question, not a platform limitation.
Your site deserves a green score
I audit your site's performance, identify the 3 priority fixes and provide an action plan — even if you're not a developer.
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